1. Field of the Invention
The present invention relates to new aqueous suspensions of mineral fillers intended, for example, for the paper industry and the use thereof in the manufacture of paper and in the manufacture of coating color for paper.
2. Discussion of the Background
In practice, aqueous suspensions of mineral fillers, the rheology of which is such that it facilitates their use, are used as part of the process of manufacturing sheet paper and cardboard by mixing them with aqueous suspensions of cellulose fibers in order to improve the opacity, whiteness or printability of the paper produced.
They are also used in all applications during which the paper is coated, and are so in the form of aqueous compounds referred to as coating colors, essentially made up of water, binders and pigments or mineral fillers.
These pigments or mineral fillers, which may of various origins, have a different affinity to water depending on their nature. A first category consists of mineral substances with a charged hydrophilic surface such as natural or synthetic calcium carbonates, in particular chalks, calcites or marbles, the dolomites or alternatively kaolins as well as calcium sulphate or titanium oxides, satin white, aluminium hydroxides or others, for example. A second category covers mineral fillers with a hydrophobic surface such as talc, mica or others, for example.
Although these two types of mineral substances do not exhibit the same rheological behavior when placed in suspension in water, particularly when prepared in high concentrations, they must nevertheless exhibit the same quality criteria for the user. The aqueous suspensions of mineral substances must therefore possess a sufficiently yield stress to avoid all risk of sedimentation as well as a high enough but not too high Brookfield viscosity to prevent any hardening of particles of the mineral substances;, so that they will be easy for the user to handle even after storage in tanks for several days without agitation. Furthermore, these suspensions must have as high a content of mineral substance as possible in order to reduce all the costs inherent in transportation due to the quantity of water present.
Previously, suspensions of mineral substances with a charged hydrophilic surface have conventionally contained dispersing agents or crushing aids consisting of polyacrylates with a low molecular weight (EP 100 947, EP 542 643, EP 542 644). However, these agents have a disadvantage in that they are not very efficient when placing in suspension and/or crushing hydrophobic substances, such as talc or mica, which are commonly used alone or in mixtures. One skilled in the art currently uses suspensions of minerals with a hydrophobic surface containing other dispersing agents and/or crushing aids, these being copolymers in which one of the monomers has a surface-active structure (EP 0 003 235, EP 215 565). These copolymers, however, have a disadvantage in that they are not efficient when it comes to placing in suspension and/or crushing mineral substances with a hydrophilic surface such as the calcium carbonates or kaolins, calcium sulphate, titanium oxides, satin white, aluminium hydroxides or others.
Consequently, until now, in order to disperse and/or crush a mineral substance with a hydrophobic surface, it has been extremely difficult for the skilled person to use a dispersing and/or crushing agent known for its efficiency in dispersing and/or as an aid for crushing mineral substances with a hydrophilic surface and vice versa.
Faced with this problem of using dispersing agents and/or a crushing aid specific to a type of mineral substance, the applicant has conducted extensive research and has developed new suspensions of mineral pigment fillers which, irrespective of the nature of the mineral substance, have the same rheological properties and contain the same dispersing agent and/or crushing aid.